published on 27 September 2012 in life

Over 7 billion people on Earth

World population hits 7 billion
Demographers have estimated that on 31 October 2011 world population reached the 7 billion mark, one billion more than 12 years before and 6 billion more than in 1800. Naturally this is just an estimate because the data available are not accurate enough to establish the exact moment in which world population reached 7 billion inhabitants, but it is a symbolic date that makes us face the issue of the demographic growth that has characterised the past century. The exponential growth of the world population is a recent phenomenon. About 2000 years ago about 300 million humans inhabited the Earth. It took over 1600 years to double this figure to 600 million. The world population reached the first billion in 1800 and since then, in just over two centuries, the population has increased seven-fold. As can be observed in the graph that shows the stages of world population growth (See graph on World population growth), the sharp increase in population growth began in the mid-20th century: in fact, since 1959, world population has been growing on average at about one billion people every 13 years. The post-war economies of developed countries grew steadily in time of peace and there was an acceleration of the industrialisation processes (as a result of post-war reconstruction). The swelling middle class was an indication of growing economic well-being. At the same time, the process of economic globalisation and the increased circulation of money, commodities and technology brought about a general improvement in human well-being even in developing countries. The quality of life increased correspondingly with the improvement in well-being. Thanks to the improvement in sanitary conditions, infant mortality rates have declined dramatically, passing from around 133 deaths per thousand births in the Fifties to 46 per thousand in the period between 2005 and 2010. The average life expectancy increased from around 48 years in the early 1950s to 70 in the first decade of the 21st century. Population growth can therefore be considered an achievement for mankind, even though one must keep in mind that not everyone gets an equal share of the benefits of this economic growth nor do they enjoy a better quality of life. In fact, there are still great inequalities among countries, in particular between industrialised and developing countries and even within countries.

Population pyramids
A population pyramid is a useful instrument to evaluate how the population of a country is evolving and to compare the demographic trends that characterise different countries. The population pyramid (or age structure diagram) is a graphical illustration used in demographic statistics that portrays the age structure of a population. Usually it consists of two horizontal bar graphs (one showing the female population, the other showing the male population) placed symmetrically back-to-back around a vertical axis, that indicates the age of the population in 5-year intervals. The x-axis indicates the number of people (or the percentage) in each age group.
The shape of the age structure diagram gives information on the demographic history of a population and indicates the demographic trend. In particular, a distinctly triangular-shaped pyramid indicates a growing population, a more rectangular-shaped age pyramid indicates rates of population growth rate around zero, and a diamond-shaped structure reflects a decreasing population.
For a better understanding of the current demographic trends, let’s analyse the age structure diagrams of Japan (See graph Population pyramid of Japan in 2011) and Nigeria (See graph Population pyramid of Nigeria in 2011), two countries with different demographic profiles, i.e. one of an industrialised country the other of a developing country. Japan’s age pyramid has the typical “spinning top” shape that indicates a declining population. In fact, in Japan, which is the country with the highest life expectancy (83 years), 23% of the population is over 65 years old and only 13% is under 15. The young population (in the fertile age range) is decreasing while the elderly population is increasing.
In Nigeria, instead, a contrasting demographic situation can be found. Nigeria’s triangular-shaped population pyramid reflects a growing population: 43% of the population is under 15 years old, while only 3% is over 65. The population pyramids of Nigeria and Japan reflect a widespread demographic tendency: developed countries have an ageing population with near zero population growth, while developing countries are contributing to world population growth. The main cause of ageing of the population in developed countries is declining fertility rates, that is, the number of children that would be born to a woman in her lifetime, along with the simultaneous rising life expectancy. In fact, the average global fertility rate has more than halved from the 1950s to today, dropping from 6 to 2.5 children per woman. This decrease is due to economic growth, development and the cultural and social changes that followed. As an example, suffice it to highlight the change in women’s role in society, thanks to a greater access to education and to paid jobs. Higher fertility rates are strongly correlated to high levels of poverty and poor access for women to education.

Future population
In its World Population Prospects: The 2010 Revision, published in May 2011, the Population Division of the United Nations Department of Economic and Social Affairs, estimated that world population will amount to 9.3 billion in 2050 and over 10 billion before the end of the century. Notwithstanding an overall decrease in fertility, in fact, at least 80 million people are added every year to the world population, a number that is equivalent to approximately the inhabitants in Germany or Ethiopia. In the next few years, the population growth shall be sustained by the countries with the highest fertility rate, most of which are in Africa, followed by Asia and Latin America. Asia, in which 60% of the present world population is concentrated, remains the macro-region with the highest population density in the world, even though Africa shall advance and its population shall triple, from one billion in 2011 to 3.6 in 2100. According to the demographic projections, the growth of the Asian population should reach a peak around mid century, and will then start to decrease. Lastly the inhabitants of America, Europe and Oceania, which are currently 1.7 billion will reach almost 2 billion by 2060 and will then decrease very slowly (they will still be about 2 billion towards the end of the century).
From the countryside to the cities: the rural exodus

According to a study carried out by the UNO, in 2008, the world’s urban population was more than the rural population for the first time. Since the first half of the 20th century, the world has witnessed a rapid urbanization of the population. From 1950 to date, in little more than sixty years, the population living in the cities has multiplied five times, passing from 745 million to 3.6 billion inhabitants, the rural population instead has shown a weaker growth rate. and in the same reference period rural population only doubled. It is estimated that in 2050 the global urban population could amount to 6 billion, out of the estimated 9.3 billion. 2 people out of 3 therefore will be living in urban centres. Instead, in the estimates for 2050 for the rural population, a mild decrease in the growth is foreseen from 3.2 billion in 2010 to 3 billion in 2050. Therefore the increase in the world population will be prevalently in the urban areas. This is a completely different picture from the previous period, in which the inhabitants of the rural areas were still prevalent, even though the population growth was mainly the urban areas. The most relevant aspect of this “urban revolution” is that the future demographic growth will be absorbed almost entirely by the urban areas of the developing countries. In the urban population map (See graph Urban population map), in fact, it is possible to observe how the urban population has varied (as a percentage of the total population) in the principal geographic areas in 1950, in 2010 and future forecasts for 2050. As it can be noted in the histograms on the map, urbanization started in the industrialized countries (North America, Europe and Oceania) and has started in the developing countries only recently. At present, in fact, in Africa and in Asia the rural population is still more than the urban population, unlike in the industrialized countries where already in 1950 most of the population lived in the cities. In the future years, instead, the trends will be inverted, as it can be observed in the map. In fact the forecasts for 2050 indicate that the phenomenon of urbanization will prevalently regard the developing countries, in particular Asia and Africa, while in the industrialized countries the urban population will increase only little.

Urbanisation and megacities
The formation of megacities* is one of the most significant urbanistic phenomena of the 21st century. In 1950, only two cities had over 10 million inhabitants (Tokyo and New York). 25 years later, in 1975, with Mexico City, the number of megacities rose to three. Today the number of megacities has risen to 23. The list of megacities is headed by Tokyo, which extends 120 km on the sea, and has a population of over 37 million inhabitants. Four cities with over 20 million inhabitants follow: Delhi with 22.7 million; Mexico City (22.8 million), New York (20.4) and Shanghai (20.2). These are followed by Sao Paolo in Brazil, Mumbai in India, Beijing in China, Dhaka in Bangladesh, Kolkata in India, Karachi in Pakistan, Buenos Aires in Argentina, Los Angeles-Long Beach-Santa Ana in the USA; Rio de Janeiro in Brazil; Manila in the Philippines; Moscow in Russia; Osaka-Kobe in Japan; Istanbul in Turkey; Lagos in Nigeria; Cairo in Egypt, Guangzhou, Guangdong in China; Shenzen in China; and Paris in France. This process is destined to continue and to develop in the future years, with a strong impact on social and economic development. It is estimated, in fact, that by 2025 there will be 37 cities with over 10 million inhabitants. In particular, none of the metropolises, for which a rapid growth is expected in the next few years, is located in an industrialised country. In 2025, out of the 37 megacities, eight will be in the industrialized countries, (two in Japan, three in Europe, three in the USA), seven in China and six in India. Not only will there be an increase in the population, but also a redistribution of human beings around the World.

* The term «megacity», according to a definition given by the United Nations, refers to an urban agglomerate with a population of over 10 million inhabitants.

Edited by Benedetta Palazzo

With the sponsorship of the Italian Ministry of Education, Universities and Research
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